Hi Dave
Think I've got this sorted for you.
In the absence of hearing from the feller at sax.co today, I spoke to Roz at Trevor James ( Tel 01622 859590 ) She's lovely and helpful and basically they have what you want in stock - she refers to the items as "mother of pearl touch pieces " and a set is 6 round 1 small 2 oval. However, don't ask me or her why, but they apparently only supply to retailers. Suggested retailers in London are Howarths (0207 935 2407) who are in Chiltern Street just off Baker Street, W1 or Chaz Foots (0207 437 1811) not sure of spelling but I know their shop in Golden Square which is near Piccadilly Circus. I know both these shops and believe they are both very reliable.
Essentially what you need to do is ask either of these retailers to place an order for you with Trevor James and she says that the maximum retail price will be £8.00 inc vat. They can send the items to you direct if the retailer gives them an email confirming where to dispatch to and they will send the sales invoice to the retailer.
Otherwise, I work in Oxford Circus and it would be no trouble for me to drop into either shop and pick them up for you and post them if you would like.
Hope this is the solution but do let me know if I can help any further.
ATB
Mike